/ab/;
/a(b)/;
/ab(c)/;
/a(bc)/;
/a(b[c])/;
/a(b|[b])/;
/a([b][c])/;
/a(b|[b]|[b])/;

/ab/;
/(a)b/;
/(a)bc/;
/(ab)c/;
/([a]b)c/;
/([a]|a)|b/;
/([a][b])c/;
/([a]|[a]|a)b/;
